Manufacture of felted fibrous sheet material of high absorptivity



Nov. 22, 1932. RlcHTER ET AL 1,888,771

MANUFACTURE OF FELTED lf'IBROUS SHEET MATERIAL OFHIGH ABSORPTIVIIY Original Filed June 14. 1927 3'Sheets-Sheet 1 e. A. RICHTER ET AL 8,771

Nov. 22, 1932.

MANUFACTURE OF FELTED FIBROUS SHEET MATERIAL OF HIGH ABS ORPTIVITY Original Filed June 14, 1927 3 Sheets-Sheet 2 a2 75%; 2/302 Way m, @J%;%

Nov. '22, 1932- e. A. RICHTER ET AL 1,838,771

MANUFACTURE OF FELTED FIBROUS SHEET MATERIAL OF HIGH ABSORPTIVITY Original Filed June-14,1927 '5 Sheets'-Sheet 5 N: flzfiwzz'm \Q /ZZZ Mal a? w Patented Nov. 2 2 1932 UNITED STATES 1,sss,771@

PATENT OFFICE GEORGE A. RICHTER AND HENRY A. CHASE, 0F BERLIN, NEW HAMPSHIRE, ASSIGNORS TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE UFACTURE 0F FELTED FIBROUS SHEET MATERIAL OF HIGH ABSOBPTIVITY Continuation of application Serial No. 198,747, filed June 14, 1927. This Serial No. 555,232.

This invention relates to the manufacture of felted fibrous sheet material, and has for its object the production of such fibrous sheet material of high absorptivity and hence par- 5 ticularly suitable for use as a base for the manufacture of uniformly impregnated products containing, if desired, high percentages of impregnating material.

In manufacturing some impregnated products, it is desirable that the fibrous base which is being impregnated be of high absorptivity in the sense that it is capable of quickly and uniformly absorbing a large amount of impregnating material; Thus, in manufacturing artificial leather by impregnating a felted, fibrous sheet. with liquid rubber, as in the form of latex, it is desirable that such sheet be capable of quickly and uniformly absorbing throughout suflicient rubber to impart the artificial leather. So, too, in the manufacture of roofing and flooring felt, it is desirable that the felt base be capable of quickly and uniformly imbibing sufficient asphalt or other waterproofing material to render the impregnated product resistant to the deteriorating effects of moisture and weathering.

We have found that a felted sheet of cellulose fiber composed of a high alpha cellulosecontaining wood fiber in substantially unbeaten or unhydrated condition and formed and dried on a paper machine, in some instances, Without the application of substantial pressure possesses surprisingly high absorptivity and is eminently suitable for use as a base in the manufacture of impregnated products, for instance those described, as a substitute for absorbent cotton in making surgical dressings, and for other purposes where felted, fibrous sheet material of high absorptivity is desirable or necessary. The

highly absorptive character of our sheet may be traced to the character of the alpha wood fiber of which it is composed, and its loosely felted, and, in some instances, substantially uncompacted condition.

The alpha wood fiber of which our sheet is composed may be prepared by alkali refining preliberated,chemical wood pulp as described necessary body, strength, and elasticity of application filed August 5, 1981.

cellulose content of about 93%, or greater.'

Or the alpha wood fiber may be prepared by processing kraft pulp with alkaline refining liquors as described in application, Serial No. 73,193, filed December 4, 1925, by George A. Richter. An alpha Wood fiber possesses the important advantage over cotton that it is less expensive and may be controlled in processing to possess substantially standard characteristics. The alpha wood fiber is preferably felted in an unbeaten or lightly beaten condition, as beating tends to diminish the absorptivity of the resulting sheet and otherwise to impair it for use as a base in impregnated products. As hereinbefore stated, the sheet is formed and dried on a papermaking machine and it may traverse the machine, Without being subjected to heavy pressure during any stage of its manufacture. To this end, a paper machine of a combined Fourdrinier and cylinder type, comprising a Fourdrinier wire traveling over a cylinder mould and 'a large rotary drier, may be used.

A better understanding of our invention may be obtained from the following more complete description thereof when taken in conjunction with the accompanying drawings, wherein Figure 1 illustrates diagrammatically one type of paper machine which may be employed in manufacturing our sheet.

Figure 2 gives curves showing the rate of absorptivity in sheets of alpha wood fiber and sulphite fiber having compactnesses falling outside of the purview of the present invention.

Figure 3 gives a curve showing the rate of absorptivity or wicking in sheets of alpha wood fiber of various compactnesses.

Referring to the drawings, l-indicates' a stock chest into which a substantiall unbeaten alpha wood fiber such as descr'l ied is fed at the desired concentration, say, as a 1% to 2% stock suspension in water. The stock suspension is removed from the chest by a pump 2 and forced through a pipe 3. to a supply tank 4, stationed above the paper machine. The stock suspension is maintained at -a constant head in the supply tank, by feeding it in sufiicient amount to overflow a baflle 5 into an overflow pipe 6, which returns such overflow to the stock chest. The stock suspension is stirred to produce a uniform suspension in the tank 4, as by an a itator a, and flows by gravity therefrom un er a regulating gate .7 into a pipe 8 leading to a cylinder-mould vat 9. The stock suspension in passing to the vat may be diluted to any desired lower consistency by introducing water in regulated amount from a water supply pipe 10 communicating with the pipe 8.

A The stock suspension flows over a bafile 20 into the vat and proceeds in the same direction as a wire 11 travelling over a cylinder mould 12 rotating in the vat. The water carrying the fiber passes through the travelling wire into the cylinder mould and out of the vat through an outlet pipe 13, thereby depositing the fiber in a uniform layer or web on the wire. The wire carrying the wet web passes over one or more suction boxes I), and also, if desired, over one or more heating units d, which serve to remove excess water from the web. The wire passes over a large rotary drier 14 which serves to dry the web completely on the wire. It is thus seen I that the web may be formed and dried with-- out being subjected to pressing or couching at any stage, and hence may remain in a loosely felted, uncompacted condition. After drying, it is removed from the wire. in sheet form and wound on a reel 24. The wire passes from the drier over guide rolls 15 and 16, and is thence directed back into the vat by a pair of guide rolls 17. Any fiber remaining on the wire is preferably removed as by a water shower just before passing into the vat.

While the stock suspension may be supplied to the vat at various consistencies, a highly dilute suspension is preferably supplied, as this ensures uniform felting and sheet texture. By drying the .web on the forming wire, transverse shrinkage of the web is diminished, as drying occurs under constraint or tension, owing to the entanglement of the web in the wire mesh. The dry sheet is soft, light, and more or less fluffy,

- and possesses phenomenally high absorptivity. The high absorptivity of the sheet may traced to the alpha wood fiber of which it is composed, and its loosely felted, and, in some 7 paper.

Alpha fiber U sual High sheet 0: surghite giaie ag resen er 0 1n in rention fiber sheet paper paper Basis weight (in lbs.), 32. 2 81 v 40 211. 0 Thickness (ininches) 0115 027 038 0225 compactness, 30 to 60 30 115 94 Absorptivlty, at least" 600 350 60 i 130 The compactness value hereinbefore given is obtained by dividing the basis weight by the thickness in inches, and multiplying by the factor 10- The expression basis welght asknown in papermaking circles represents the weight in pounds of 480 sheets whose dimensions are 24 x 36 inches, this being equivalent to 2,880 square feet of sheet material. In other'words, the compactness value really represents the weight of fiber per unit volume of sheet material. The absorptivity was ascertained by noting the water crawl up a strip, the values given denoting hundredths inches crawl on the strip in five minutes. It is to be observed that the compactness of the sheet of the present invention is far less, and that its absorptivity is phenomenally greater than that of a sulphite fiber paper or even of a high grade rag blotting paper, v

and that it is also slightly ss compact an far more absorptive'than a similar sulphite fiber sheet. Our sheet is therefore an excellent base for the manufacture of impregnated products, such, for example, as the artificial leather described and claimed in application, Serial No. 17 5,946, filed March 16, 1927, by George. A. Richter, or for other uses where fibrous material of highabsorptivity is desired.

We cannot account for the phenomenal absorptivity or capillarity whichwe secure in our product except in terms of its interfelted, waterlaid texture and its particular compactness, coupled with certain properties which a substantially unbeaten, refined wood pulp of an alpha cellulose content of at least about 93% is known to possess. Among the properties of such refined wood pulp is its far greater freedom from fiber fragments and colloidal cellulose, as well asfrom hemicelluloses and resins, than unrefined wood pulp of the character of sulphite, kraft, or the like. ,When the fibers'of refined wood pulp are well beaten to generate gelatinized or colloidal cellulose and then formed into a sheet of'unsized paper, the resulting paper is not much different in its absorptivity from pafipers made in the same way from an unre ned wood pulp. So, too, when the substantially unbeaten or unhydrated wood pulps are formed into sheets whose compactness falls materially outside of the range of compactness of our product, it makes little difi'erence in so far as concerns rate of ab- 71, and the other for a sheet of unbeaten sulphite pulp having a compactness of 74.

The ordinates represent the wicking effect. or water crawl, and the abscissae the time,

elapsed. These curves practically coincide over a five-minute period. The refined wood pulp curve is ly slightly above that ofthe sulphite pulp curve, even though the refined wood pulp sheet was of three units lower compactness than the sulphite pulp sheet. In

securing the data for drawing the curves, strlps were cut from the sheet material and dot-marked with an indelible encil at various distances from one end. ach strip was then immersed to the first dot in water at 20 C. and the time in seconds for the water to rise various distances; denoted by change in color of the indelible dots, was recorded as the wicking effect or absorptivity. This method was found reliable and capable of being checked. Within wide limits, the width of the strip did affect the Wicking effect or absorptivity.

When loose or flufied dry pulp is, as such, formed into layers or sheets having a com; pactness much lower than our product, for instance a form comparable to so-called absorbent cotton or cotton batting, one does not realize much more absorptivity in the case of a' refined wood pulp such as We use than in the case of the usual commercial sulphite pulp having an alpha cellulose content of about 87%, even though such sheets of re- .fined wood pulpare primarily, on accountof their purity, softness and stability, better suited for surgical dressings. Thus, absorptivity tests performed on sheets fabricated in a dry way from refined wood pulp and sheets similarly fabricated from sulphite.

pulp gave the following results Wicking effect time in seconds to rise 2 inches Refined wood pulp a1 sulphite pulp 35 The refined wood pulp was similar to that used in our product but the sheets formed with this material and with the sulphite pulp had a compactness of about 8. It is thus seen that in sheet form other than that of the present invention, a refined wood pulp is not at all strikingly more absorptive than is an unrefined wood pulp. This conclusion is further well borneoutby the curve given in Figure 3 for the absorptivity orwicking rate in sheets of alpha wood fiber of various compaotnesses, The wicking rate represented by the ordinates is given in terms of seconds for a 2-inchrise or crawl of water up strips, cut from the sheets of various compactnesses. The sheets were all made of an alpha wood fiber such as we use in producing our product. It is to be observed that the curve is sharply descending in the regions of low compactness, becomes comparatively flat or I has minimum curvature in the region of compactness of our product, and is sharply ascending in the region of high compactness.

In other words, when one departs materially in either direction from the compactness region whereinto our product falls, he avails himself so little of the quality of absorbency inherent in a refined wood pulp that such pulp is little better in this quality than is an unrefined wood pulp. Our product, on the other hand, is one in which maximum advantage is taken of the quality of absorbency 1n refined wood pulp. Maximum absorbency or lcapillarity is a prime desideratum, for instance, when the sheet is to be impregnated with rubber latex. In such case, the latex penetrates our sheet so quickly and so uniformly that it is a simple matter to secure complete and uniform impregnation even when a continuous sheet of our product is moved 'progressively through a bath of the latex quickly and with but a short stretch of the sheet water-dispersed materials, such as I immersed in the bath. At the same time, our

sheet has sufiicient integrity so that it can be safely handled and impregnated.

In the region of compactness of our sheet, i. e., weight of wood pulp per unit volume of sheet, there is a certain percentage of void space in the sheet. This space is not continuous, but is made up of interstices or canals which, if evidently kept at a certain size, are conducive to high capillarity or absorptivity in the sheet. In the case of our sheet, which is fabricated from substantially unbeaten wood pulp of an alpha cellulose content of at least about 93% containing a relatively slight amount of fiber fragments, colloidal cellulose, resinous matter, and the like, the capillary interstices or canals in the sheet evidently remain open to promote maximum capillary action, whereas such action is evidently greatly impeded in a similar sheet fabricated from unrefined wood pulp, such as sulphite, on ac-v count of fiber fragments, colloidal cellulose, and resinous matter entering into the capillary'interstices and canals and altering their dimensions from optimum value. Moreover, a similar sulphite pulp sheet shrinks to a greater extent during drying; and colloidal and water-soluble materials being present in greater amount, tend to diffuse or migrate to the surface, where evaporation of water is taking )place, and thus to clog the surface pores, as attested by a skin formation or case hardening on such a sheet. These latter factors, too, are evidently partially responsible for the vastly inferior absorptivity of the sulphite pulp sheet. In other words,where the interstitial spaces in the sheet are exceedingly small, as in a highly compacted sheet, or

where the interstitial spaces are comparatively large, as in loose, bulk pulp with a random fiber arrangement, the character of the pulp is evidently of little importance in determining absorptivity. In the case -of a waterlaid sheet of loosely interfelted wood fibers,

however, and more especially of a sheet possessing a compactness of about to 60, a refined wood pulp of an alpha cellulose content of at least about 93% gives a product of suprisingly high ab'sorptivity or capillarity.

In attaining the compactness values in the felts of the present invention, and more particularly those values at the lower end of the range hereinbefore given, it may, as already indicated, be necessary, to dispense -practically entirely with the use of pressure devices on the papermaking machine. This is especially true when the pulp used as raw ma terial is a refined sulphite pulp whose refinment has been brought about in hot, comparatively dilute, alkaline liquors, as disclosed in aforementioned application Serial No. 716,154, filed May 27, '1924, by George A. Richter and Milton 0. Schur. Felts of such low compactness are of great value in making bituminized sheets for roofing and analogous purposeswhere a maximum bitumen or asphalt content is desired, and 1n making other impregnated products wherem a maximum content of impregnant is desired. On the other hand, when the pulp has been refined in comparatively cold, concentrated alkaline liquors, as disclosed in aforementioned application Serial No. 73,193, filed December 4., 1925, by George A. Richter, the felts fabricated from such pulp tend to be bulkier and at least about 93%.

ent invention, we do notherein claim specifically the use of unbleached pulps for this purpose, as this constitutes a separate invention disclosed and claimed in application Serial No. 580,496, filed December 11, 1931, by

George A. Richter. Impregnated products containing the felted base of the present invention are characterized by-highly desirable characteristics attributable to the refined but substantially unhydrated, chemically preliberated, cellulose pulp which has entered thereinto as a principal raw material. Thus, bituminized sheets containing an alkali-refined but substantially unhydrated wood pulp as a principal raw material are possessed of a tear resistance conspicuously greater than a product containing a cotton or rag felt base, being, in fact, practically tear proof. We do not, however herein claim such bituminized sheets, for this subject matter is. disclosed and claimed in our application Serial No. 570,034, filed October 20, 1931.

So far as certain subject matter" is concerned, this is a continuation of our application, Serial No. 198,747, filed J unue 14, 1927.

' We claim:

1. A water-laid sheet of loosely felted, substantially uncompacted and unbeaten wood pulp having an alpha cellulose content of at least about 93%, said sheet having an absorptivity of at least about six inches in terms of water crawl up a strip in five minutes.

2. A water-laid sheet of looselyfelted and substantially unbeaten wood pulp having an alpha cellulose content of at least about 93%, said sheet having a compactness value falling between about 30 and 60 in terms of basis weight divided by thickness in inches and multiplied by the factor 10 ,3. A water-laid sheet of loosely felted, substantially unbeaten wood pulp having an alpha cellulose content of at least about.93%,

said sheet having a compactness value falling.

between about 30 and 60 in terms of basis weight divided by thickness in inches and multiplied by the factor 10?, and said sheet having an absorptivity of at least about six inches in terms of water crawl up a strip in five minutes.

4. A bulky, highly absorptive, water-laid sheet of loosely felted and substantially 11nhydrated, chemically preliberated cellulose pulp, refined to an alpha cellulose content of 5. A highly absorptive, waterlaid felt containing as a principal raw material substantially unhydrated, preliberated wood pulp refined to an alpha cellulose content of at least about 93%.

6. A highly absorptive waterlaid felt conizo taining as a principal raw material substane tially' unhydrated, chemically preliberated wood pulp refined by'alkalito a higher alpha signatures.

cellulose content than that present therein at the time of its liberation.

7. A. process which comprises liberating cellulose pulp from raw cellulosic material, refining such pulp in an alkaline liquor to a higher alpha cellulose content, and making felt from such refined pulp in a substantially unhydrated condition.

8. A process which comprises refining pre- I liberated wood pulp in an alkaline liquor to a higher alpha cellulose content, and making a waterlaid felt from a furnish containing such refined pulp in substantially unhydrated condition. y 9. A process which comprises refining preliberated chemical wood pulp in an alkaline liquor to an alpha cellulose content of at least about 93%, and making from a furnish containing such refined Wood pulp in a substantially unhydrated condition, a waterlaid felt whose compactness value falls between about 30 and 60 in terms of basis weight divided by thickness in inches and multiplied by the factor 10*.

In testimony whereof we have aflixed our GEORGE A. RICHTER. HENRY A. CHASE. 

